题目

—Tom will come to see his father whenever it is ____ for him. —That's because his father is very old and weak now. A . private B . polite C . absent D . convenient 答案：DX、Y是元素周期表ⅦA族中的两种元素。下列叙述能说明X的非金属性比Y强的是（    ）A.X原子的电子层数比Y原子的电子层数多B.X的氢化物的沸点比Y的氢化物的沸点低C.X的气态氢化物比Y的气态氢化物稳定D.Y的单质能将X从NaX的溶液中置换出来